Communication system

ABSTRACT

A communication system capable of communicating control information without decreasing the bandwidth available to users. A coder encodes a primary signal to generate encoded data such that the polarity of the encoded data alternates between positive and negative polarities. A polarity-reversed data generator reverses the polarity of part of the encoded data to generate polarity-reversed data. A transmitter transmits, as communication data, the encoded data including the polarity-reversed data. A receiver receives the communication data, and a polarity-reversed data detector determines whether or not the polarity of the received communication data alternates between positive and negative polarities, and detects, as the polarity-reversed data, data of which the polarity differs from an expected polarity. A polarity recognizer recognizes the polarity of the polarity-reversed data and treats the recognized polarity as control information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefits of priority fromthe prior Japanese Patent Application No. 2006-221347, filed on Aug. 15,2006, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to communication systems, and moreparticularly, to a communication system for exchanging communicationdata.

2. Description of the Related Art

In conventional network systems such as Ethernet (registered trademark)systems, control information relating to control of device operations,such as alarm/fault information and device status notificationinformation, is generally transmitted by using part of channel resourcesallocated to user packets.

FIGS. 10A and 10B illustrate the concepts of how control information istransmitted in conventional systems. When control information istransmitted to a device within a network to control the device, thecontrol information is assembled into a control information packet andinserted between user packets, as shown in FIG. 10A, or the controlinformation is carried by the header of a packet, as shown in FIG. 10B.

As conventional techniques related to transmission of controlinformation, a technique has been proposed in which control informationis encoded and transmitted in such a manner that code words with neutralpolarity and code words with non-neutral polarity do not exactlycoincide in position (e.g., Japanese Unexamined Patent Publication No.2002-217738 (paragraph nos. [00241] to [0029], FIG. 1)).

When control information is exchanged between devices in theconventional systems, however, part of the channel resources allocatedto user packets is used to communicate the control information, as shownin FIGS. 10A and 10B, giving rise to a problem that the bandwidthavailable to users decreases by an amount corresponding to the controlinformation.

SUMMARY OF THE INVENTION

The present invention was created in view of the above circumstances,and an object thereof is to provide a communication system capable ofcommunicating control information without decreasing the bandwidthavailable to users.

To achieve the object, there is provided a communication system forcommunicating data. The communication system comprises a transmittingdevice and a receiving device. The transmitting device includes a coderfor encoding data of a primary signal to generate encoded data such thatpolarity of the encoded data alternates between positive and negativepolarities, a polarity-reversed data generator for reversing thepolarity of part of the encoded data to generate polarity-reversed data,and a transmitter for transmitting, as communication data, the encodeddata including the polarity-reversed data. The receiving device includesa receiver for receiving the communication data, a polarity-reverseddata detector for determining whether or not polarity of the receivedcommunication data alternates between positive and negative polarities,and detecting, as the polarity-reversed data, data of which the polaritydiffers from an expected polarity, and a polarity recognizer forrecognizing the polarity of the polarity-reversed data and treating therecognized polarity as control information.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings which illustrate preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the principle of a communication system.

FIG. 2 illustrates operation according to a first embodiment of theinvention.

FIG. 3 shows an example of polarity reversal from positive to negativepolarity.

FIG. 4 illustrates operation according to a second embodiment.

FIG. 5 illustrates operation according to a third embodiment.

FIG. 6 illustrates operation according to a fourth embodiment.

FIG. 7 shows a case where an error response has been received.

FIG. 8 illustrates the principle of a communication system.

FIG. 9 illustrates operation of the communication system.

FIGS. 10A and 10B illustrate the concepts of how control information istransmitted in conventional systems.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings. FIG. 1 illustrates theprinciple of a communication system. The communication system 1comprises a transmitting device 10 and a receiving device 20 andperforms, for example, Ethernet communication. In the figure, thetransmitting device 10 and the receiving device 20 are separatelyillustrated; in practice, a single communication device functions asboth the transmitting and receiving devices 10 and 20.

The transmitting device 10 includes a coder 11, a polarity-reversed datagenerator 12, and a transmitter 13. The coder 11 encodes the data of aprimary signal to generate encoded data such that the polarity of theencoded data alternates between positive and negative polarities.

The polarity-reversed data generator 12 reverses the polarity of part ofthe encoded data to generate polarity-reversed data. The transmitter 13transmits, as communication data, the encoded data including thepolarity-reversed data.

The receiving device 20 includes a receiver 21, a polarity-reversed datadetector 22, a polarity recognizer 23, and a controller 24. The receiver21 receives the communication data. The polarity-reversed data detector22 determines whether or not the polarity of the received communicationdata alternates between positive and negative polarities, and detects,as the polarity-reversed data, data of which the polarity differs fromthe expected polarity. The polarity recognizer 23 recognizes thepolarity of the polarity-reversed data and treats the recognizedpolarity as control information. The controller 24 controls thereceiving device 20 in accordance with the control information.

The coder 11 generates the encoded data by converting the primary signaln bits by n bits into an m-bit data unit (n<m) whose polarity alternatesbetween positive and negative polarities. In the following description,it is assumed that n and m are 8 and 10, respectively, so that 8B/10Bconversion is performed.

The following is a brief explanation of the 8B/10B conversion. The8B/10B conversion is an encoding scheme employed especially in GigabitEthernet such as 1000BASE-LX, 1000BASE-SX and 1000BASE-CX or in FiberChannel, wherein a pattern is selected from within the 10-bit code spaceso that 0s and 1s may be almost equal in number, and 8-bit code isconverted to 10-bit code for transmission and vice versa for reception.

When converting 8-bit data to 10-bit data, the balance of the 0s and 1scontained in the data is suitably adjusted to thereby enable recovery ofthe data signal with reduced bit error rate as well as recovery of theclock signal embedded in the data signal.

If, at this time, the bits 0 and 1 are simply allotted high and lowsignal voltages for transmission, the signal level remains unchanged incases where there is a succession of 0s or 1s, possibly making thereceiving side fail to achieve self-synchronization. To avoid theinconvenience, the occurrences of 0s and 1s are made even to adjust thedirect-current balance (reduce the direct-current component), therebypreventing repetition of an identical state and enabling stablecommunications.

The communication system 1 to which a first embodiment of the inventionis applied will be now described with reference to FIG. 2 illustratingthe operation of the first embodiment. Let us suppose that thetransmitting device 10 transmits data 00-01-02-03-04-05 (h) as theprimary signal to the receiving device 20.

S1: The coder 11 subjects the data 00-01-02-03-04-05 (h) to 8B/10Bconversion (e.g., 8-bit code is converted to 10-bit code by using an8B/10B conversion table or the like prepared beforehand).

In this instance, 00 is converted to 100111 0100 (−), 01 to 100010 1011(+), 02 to 101101 0100 (−), 03 to 110001 0100 (+), 04 to 110101 0100(−), and 05 to 101001 0100 (+). Each sign enclosed in parenthesesindicates the polarity of data. The conversion is carried out such thatthe polarity begins with negative polarity (−) as an initial value andthereafter alternates between positive (+) and negative (−) polarities.

S2: The polarity-reversed data generator 12 reverses the polarity ofpart of the encoded data. In FIG. 2, the polarity of 101101 0100 (−),which is the 10B data of 02, is reversed, thus obtaining 010010 1011(+).

S3: The transmitter 13 transmits communication data including thepolarity-reversed data 010010 1011 (+), and the receiver 21 receives thecommunication data.

S4: The polarity-reversed data detector 22 determines whether or not thepolarity of the received communication data alternates between positiveand negative polarities, and detects, as the polarity-reversed data,data of which the polarity differs from the expected polarity.

In this instance, the communication data is received in the order:100111 0100 (−)→100010 1011 (+) →010010 1011 (+)→110001 0100 (+)→1101010100 (−)→101001 0100 (+). The third data 010010 1011 (+), which is the10B data of 02, has polarity different from the expected polarity, andtherefore, this data is detected as the polarity-reversed data.

S5: The polarity recognizer 23 determines whether the polarity of thepolarity-reversed data is reversed in the positive-to-negative directionor vice versa, and treats 1-bit information indicated by the determinedreversal direction as control information for the receiving device 20.

For example, if data with the polarity (+) is input at the timing whenthe polarity (−) is expected, this polarity reversal direction isrecognized as the control information “1”. On the other hand, if datawith the polarity (−) is input at the timing when the polarity (+) isexpected, the polarity reversal direction is recognized as the controlinformation “0”. In the example of FIG. 2, data with the polarity (+) isreceived at the timing when the polarity (−) is expected, and therefore,the control information “1” is derived.

FIG. 3 shows an example of polarity reversal from the positive tonegative polarity. In the figure, the polarity of the data 110001 0100(+), which is the 10B data of 03, is reversed, thus obtaining 0011101011 (−) As a result, the control information “0” is derived.

In the example shown in FIG. 2, “1” is obtained as the controlinformation, and the controller 24 performs a predetermined controlaction in accordance with the control information “1”. For example,prearrangement is made such that the control information “1” indicates anotification of fault occurrence, and when the control information “1”is received from the transmitting device 10, the controller 24 executesan appropriate process to cope with the fault occurring in thetransmitting side.

Thus, in the first embodiment, the polarity of data is reversed so thatthe polarity-reversed data may be used as the control information. It istherefore unnecessary to insert control information in user channelresources, and the control information can be transmitted as a polaritychange of the primary signal. Accordingly, the bandwidth available tousers does not decrease at all and yet the control information can betransferred between the transmitting and receiving devices, making itpossible to improve communication quality.

After the control information is derived from the polarity reversaldirection of the polarity-reversed data, the receiving device 20 againreverses the polarity of the polarity-reversed data to recover theoriginal data, that is, the data 010010 1011 (+) is reversed in polarityas 101101 0100 (−), so that the data 101101 0100 (−) corresponding to 02may be used as user data. The receiving device 20 then performs 10B/8Bconversion, thus obtaining 00-01-02-03-04-05 (h).

The communication system 1 to which a second embodiment of the inventionis applied will be now described. In the second embodiment, the firstpolarity-reversed data is recognized as a control information starttrigger, and the polarities of the succeeding k (=1, 2, . . . ) units of10B data are treated as the control information.

FIG. 4 illustrates operation according to the second embodiment. It isassumed here that the transmitting device 10 transmits data00-01-02-03-04-05 (h) as the primary signal to the receiving device 20.

S11: The coder 11 subjects the data 00-01-02-03-04-05 (h) to 8B/10Bconversion, so that 00 is converted to 100111 0100 (−), 01 to 1000101011 (+), 02 to 101101 0100 (−), 03 to 110001 0100 (+), 04 to 1101010100 (−), and 05 to 101001 0100 (+). The conversion is carried out suchthat the polarity begins with negative polarity (−) as an initial valueand thereafter alternates between positive (+) and negative (−)polarities.

S12: The polarity-reversed data generator 12 generates polarity-reverseddata by reversing the polarity of at least one unit of 10B data. In FIG.4, the polarity of 101101 0100 (−), which is the 10B data of 02, isreversed, thus obtaining 010010 1011 (+). Further, the polarity of110101 0100 (−), which is the 10B data of 04, is reversed, thusobtaining 001010 1011 (+).

S13: The transmitter 13 transmits communication data including thepolarity-reversed data 010010 1011 (+) and 001010 1011 (+), and thereceiver 21 receives the communication data.

S14: The polarity-reversed data detector 22 determines whether or notthe polarity of the received communication data alternates betweenpositive and negative polarities, and detects, as the polarity-reverseddata, data of which the polarity differs from the expected polarity.

In this instance, the communication data is received in the order:100111 0100 (−)→100010 1011 (+) →010010 1011 (+)→110001 0100 (+)→0010101011 (+)→101001 0100 (+). The third data 010010 1011 (+), which is the10B data of 02, and the fifth data 001010 1011 (+), which is the 10Bdata of 04, have polarity different from their expected polarity, andtherefore, these two units of data are detected as the polarity-reverseddata.

S15: The polarity recognizer 23 recognizes the first detectedpolarity-reversed data as the control information start trigger andtreats the polarities of the succeeding k units of 10B data as thecontrol information. The value of k is determined beforehand.

Where k=2, for example, the first polarity-reversed data 010010 1011 (+)corresponding to 02 is recognized as the control information starttrigger, and the polarities of the two units of 10B data (20(=2×10) bitsin total) succeeding 02 and corresponding to 03 and 04, respectively,are treated as the control information.

Assuming that the polarity identical with the expected polarityindicates “1” and that the polarity different from the expected polarityindicates “0”, the polarities of the two units of 10B data correspondingto 03 and 04 show “10” as the control information. In accordance withthe control information “10”, the controller 24 performs a predeterminedcontrol action.

With reference to the aforementioned Step S12, it is stated that “thepolarity-reversed data is generated by reversing the polarity of atleast one unit of data.” The expression “at least one unit of data” isused because the polarity of one unit of 10B data needs to be reversedso as to indicate the control information start trigger and also becauseit is likely that the polarities of the succeeding units of data happento agree with the contents of the control information to be communicatedand thus need not be reversed.

Thus, in the second embodiment, the first detected polarity-reverseddata is recognized as the control information start trigger, and thepolarities of the k units of 10B data succeeding the polarity-reverseddata are treated as the control information. With this configuration,the amount of the control information can be increased.

The communication system 1 to which a third embodiment of the inventionis applied will be now described. In the third embodiment, the sameprocess as in the second embodiment is executed, and in addition, anerror-correcting code (e.g., parity check code) is added at the end ofthe control information to check normalcy of data transmission.

FIG. 5 illustrates operation according to the third embodiment. It isassumed here that the transmitting device 10 transmits data00-01-02-03-04-05 (h) as the primary signal to the receiving device 20.

S21: The coder 11 subjects the data 00-01-02-03-04-05 (h) to 8B/10Bconversion, so that 00 is converted to 100111 0100 (−), 01 to 1000101011 (+), 02 to 101101 0100 (−), 03 to 110001 0100 (+), 04 to 1101010100 (−), and 05 to 101001 0100 (+). The conversion is performed suchthat the polarity begins with negative polarity (−) as an initial valueand thereafter alternates between positive (+) and negative (−)polarities.

S22: The polarity-reversed data generator 12 generates polarity-reverseddata by reversing the polarity of at least two units of 10B data. InFIG. 5, the polarity of 101101 0100 (−), which is the 10B data of 02, isreversed, thus obtaining 010010 1011 (+), and the polarity of 1101010100 (−), which is the 10B data of 04, is reversed, thus obtaining001010 1011 (+). Further, the polarity of 101001 0100 (+), which is the10B data of 05, is reversed, thus obtaining 010110 1011 (−). Thepolarity-reversed data corresponding to 02 indicates the controlinformation start trigger, while the polarity-reversed datacorresponding to 05 is used as error-correcting code data.

S23: The transmitter 13 transmits communication data including thepolarity-reversed data generated in Step S22, and the receiver 21receives the communication data.

S24: The polarity-reversed data detector 22 determines whether or notthe polarity of the received communication data alternates betweenpositive and negative polarities, and detects, as the polarity-reverseddata, data of which the polarity differs from the expected polarity.

In this instance, the communication data is received in the order:100111 0100 (−)→100010 1011 (+) →010010 1011 (+)→110001 0100 (+)→0010101011 (+)→010110 1011 (−). The third data 010010 1011 (+), which is the10B data of 02, the fifth data 001010 1011 (+), which is the 10B data of04, and the sixth data 010110 1011 (−), which is the 10B data of 05,have polarities different from their respective expected polarities, andtherefore, these three units of data are detected as thepolarity-reversed data.

S25: The polarity recognizer 23 recognizes the first detectedpolarity-reversed data as the control information start trigger andtreats the polarities of the succeeding k (=1, 2, . . . ) units of10-bit data as the control information. The value of k is determined inadvance.

Where k=2, for example, the first polarity-reversed data 010010 1011 (+)corresponding to 02 is recognized as the control information starttrigger, and the polarities of the two units of 10B data (20(=2×10) bitsin total) succeeding 02 and corresponding to 03 and 04, respectively,are treated as the control information.

Assuming that the polarity identical with the expected polarityindicates “1” and that the polarity different from the expected polarityindicates “0”, the polarities of the two units of 10B data correspondingto 03 and 04 show “10” as the control information. In accordance withthe control information “10”, the controller 24 performs a predeterminedcontrol action.

Further, the polarity recognizer 23 recognizes the (k+1)th data, thatis, the polarity-reversed data 010110 1011 (−) which is the third datafollowing the start trigger and corresponding to 05, as theerror-correcting code data and checks normalcy of the transmission lineby means of this code.

For example, odd parity check is adopted (in which the transmitting sidetransmits data with the sum of 1s set to an odd number, and thereceiving side judges the transmission line to be normal if the sum of1s in the received data is odd, and judges the transmission line to beanomalous if the sum of 1s is even). In the example shown in FIG. 5, thesum of 1s in the data 010110 1011 (−) corresponding to 05 is “6”, andtherefore, the transmission line is judged to be anomalous. In thiscase, the control information “10” and the 10B data forming the primarysignal are regarded as invalid.

With reference to the aforementioned Step S22, it is stated that “thepolarity-reversed data is generated by reversing the polarity of atleast two units of data.” The expression “at least two units of data” isused because the polarity of two units of 10B data needs to be reversed,one to indicate the control information start trigger and the other toinclude the error-correcting code, and also because it is likely thatthe polarities of the intervening units of data happen to agree with thecontents of the control information to be communicated and thus need notbe reversed.

In this manner, the third embodiment is configured to perform thefunction of the second embodiment, and besides, the error-correctingcode such as a parity check code is included in the communication datato be transmitted. This permits the receiving device 20 to correct errorin the control information, making it possible to prevent erroneoustransmission of the control information.

The communication system 1 to which a fourth embodiment of the inventionis applied will be now described. In the fourth embodiment, a responsemessage indicative of reception of data is transmitted by using thepolarity of communication data.

FIG. 6 illustrates operation according to the fourth embodiment. Let usconsider the case where certain data has been sent from the receivingdevice 20 to the transmitting device 10, and in response to the datareceived, the transmitting device 10 transmits a response message,together with a primary signal 00-01-02-03-04-05 (h), to the receivingdevice 20 by making use of the polarity of the primary signal.

S31: The coder 11 subjects the data 00-01-02-03-04-05 (h) to 8B/10Bconversion, so that 00 is converted to 100111 0100 (−), 01 to 1000101011 (+), 02 to 101101 0100 (−), 03 to 110001 0100 (+), 04 to 1101010100 (−), and 05 to 101001 0100 (+). The conversion is carried out suchthat the polarity begins with negative polarity (−) as an initial valueand thereafter alternates between positive (+) and negative (−)polarities.

S32: To send a response message to the receiving device 20 in reply tothe data received therefrom, the polarity-reversed data generator 12generates polarity-reversed data by reversing the polarity of one unitof 10B data to indicate a response message start trigger, which is thestart position of the response message.

Then, the polarity of the 10B data unit immediately following theresponse message start trigger is left unreversed if a normal responsemessage (ACK) is to be transmitted, and is reversed if an error responsemessage (NACK) is to be transmitted.

In the illustrated example, the polarity of 101101 0100 (−), which isthe 10B data of 02, is reversed as the response message start trigger,thus obtaining 010010 1011 (+). Assuming that a normal response message(ACK) is to be transmitted, the polarity of the 10B data correspondingto 03 is left unreversed.

S33: The transmitter 13 transmits the communication data processed inStep S32, and the receiver 21 receives the communication data.

S34: The polarity-reversed data detector 22 determines whether or notthe polarity of the received communication data alternates betweenpositive and negative polarities, and detects, as the polarity-reverseddata, data of which the polarity differs from the expected polarity.

In this instance, the communication data is received in the order:100111 0100 (−)→100010 1011 (+) →010010 1011 (+)→110001 0100 (+)→1101010100 (−)→101001 0100 (+). The third data 010010 1011 (+) has polaritydifferent from the expected polarity, and therefore, this data isdetected as the polarity-reversed data.

S35: The polarity recognizer 23 recognizes the first detectedpolarity-reversed data as the response message start trigger anddetermines whether the polarity of the 10B data immediately followingthe polarity-reversed data shows a normal response indicative of normaltransmission of data or an error response indicative of transmissionerror.

Assuming that the polarity identical with the expected polarityindicates control information “1” as the normal response and that thepolarity different from the expected polarity indicates controlinformation “0” as the error response, the polarity of the 10B data110001 0100 (+) immediately following the first detectedpolarity-reversed data and corresponding to 03 shows the controlinformation “1” since it is identical with the expected polarity. Basedon the control information “1”, therefore, it is concluded that the datawas normally transmitted.

FIG. 7 shows the case where an error response has been received. The 10Bdata corresponding to 03 is 001110 1011 (−), that is, the polarity ofthe 10B data has been reversed and differs from the expected polarity.Accordingly, the control information “0” indicative of error response isderived.

Thus, in the fourth embodiment, the polarity of the primary signal isutilized to transmit the response message start trigger, which indicatesthe start of a response message responsive to the data received, as wellas the ACK or NACK message. It is therefore possible to determinewhether or not data has been normally transmitted. For example, normalcyof data transmission may be determined based on the parity check codeused in the third embodiment, and a response message indicating thedetermination result may be transmitted by using the function of thefourth embodiment.

A modification of the communication system 1 will be now described withreference to FIG. 8 illustrating the principle thereof. A communicationsystem 2 comprises a transmitting device 30 and a receiving device 40.The transmitting device 30 includes a coder 31, a head timing assigner32, a polarity processor 33, and a transmitter 34.

The coder 31 encodes the data of a primary signal to generate encodeddata such that the polarity of the encoded data alternates betweenpositive and negative polarities. The head timing assigner 32 assigns,to the encoded data, head timing indicative of the head, or beginning,of the encoded data.

With respect to k units of data succeeding the head timing, the polarityprocessor 33 performs a process such that the polarities of the k dataunits are individually reversed or left unreversed. The transmitter 34transmits, as communication data, the encoded data to which the headtiming has been assigned and of which the polarity has been processed bythe polarity processor 33.

The receiving device 40 includes a receiver 41, a head timing detector42, and a polarity reversal/non-reversal detector 43. The receiver 41receives the communication data, and the head timing detector 42 detectsthe head timing from the communication data.

The polarity reversal/non-reversal detector 43 determines whether or notthe polarities of the k data units succeeding the head timing alternatebetween positive and negative polarities. Then, the polarity differentfrom the expected polarity is detected as a polarity reversal valuewhile the polarity identical with the expected polarity is detected as apolarity non-reversal value, and polarity data constituted by at leastone of the polarity reversal and non-reversal values is treated ascontrol information.

Operation of the communication system 2 will be now explained withreference to FIG. 9. It is assumed here that the transmitting device 30transmits data 00-01-02-03-04-05 (h) as the primary signal to thereceiving device 40. Also, the transmitting device 30 transmits BC andC5 as inter-packet gap data (idle) and FC as SOP (Start Of Packet)indicating the start of a packet.

S41: The coder 31 subjects the data 00-01-02-03-04-05 (h) to 8B/10Bconversion, so that 00 is converted to 100111 0100 (−), 01 to 1000101011 (+), 02 to 101101 0100 (−), 03 to 110001 0100 (+), 04 to 1101010100 (−), and 05 to 101001 0100 (+). The conversion is carried out suchthat the polarity begins with negative polarity (−) as an initial valueand thereafter alternates between positive (+) and negative (−)polarities.

S42: With respect to the k units of data succeeding the head timing, thepolarity processor 33 performs a process such that the polarities of thek data units are individually reversed or left unreversed. In FIG. 9,the polarity of 101101 0100 (−), which is the 10B data of 02, isreversed, thus obtaining 010010 1011 (+).

S43: The head timing assigner 32 generates 110000 0111 (+), which is 10Bdata corresponding to FC, as SOP indicating the start of a packet.

S44: The transmitter 34 transmits 110000 0101 (+), which is 10B datacorresponding to BC, and 101001 0110 (−), which is 10B datacorresponding to C5, in the intervals where no packet data exists. Also,the transmitter attaches 110000 0111 (+), which is 10B datacorresponding to FC and serving as the SOP indicating the start ofpacket data, to the encoded data and transmits, as communication data,the encoded data whose polarity has been processed by the polarityprocessor 33. The receiver 41 receives the communication data.

S45: The head timing detector 42 detects the SOP.

S46: The polarity reversal/non-reversal detector 43 determines whetheror not the polarity of the received packet data alternates betweenpositive and negative polarities, and treats the polarities of the kunits of 10B data succeeding the SOP as the control information. Thevalue of k is determined beforehand.

Where k=3, for example, the polarities of the three units of 10B data(30(=3×10) bits in total) succeeding the SOP and corresponding to 00, 01and 02 are treated as the control information.

The polarity identical with the expected polarity may be recognized asthe polarity non-reversal value “1” while the polarity different fromthe expected polarity may be recognized as the polarity reversal value“0”, and in this case, the polarities of the three units of 10B datacorresponding to 00, 01 and 02 show the control information “110”.

Thus, the communication system 2 detects the SOP not only as the packetstart trigger but as the control information start trigger and treatsthe polarities of the k units of 10B data succeeding the SOP as thecontrol information.

In the case of assembling the encoded data into packets with thisconfiguration, it is possible, for example, to cause the head timingassigner 32 to assign the head timing to each of packets p1, p2, . . . ,and to cause the polarity processor 33 to include, in the differentpackets p1, p2, . . . , control information c1, c2, . . . correspondingthereto.

In this case, packets may be generated such that the polarities of thethree units of 10B data succeeding the head timing of the packet p1indicate the control information while the polarities of the four unitsof 10B data succeeding the head timing of the packet p2 indicate thecontrol information, to thereby enable the polarityreversal/non-reversal detector 43 of the receiving device 40 to acquiredifferent polarity data on the packets p1, p2, . . . as their controlinformation.

In the communication system of the present invention, the transmittingdevice encodes the primary signal to generate encoded data such that thepolarity of the encoded data alternates between positive and negativepolarities, and reverses the polarity of part of the encoded data togenerate polarity-reversed data. At the receiving device, it isdetermined whether or not the polarity of received communication dataalternates between positive and negative polarities, data havingpolarity different from the expected polarity is detected as thepolarity-reversed data, and the polarity of the polarity-reversed datais treated as control information. Thus, since the control informationcan be communicated between the transmitting and receiving deviceswithout decreasing the bandwidth available to users, all channelresources can be devoted to user data, making it possible to improvecommunication quality.

The foregoing is considered as illustrative only of the principles ofthe present invention. Further, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and applications shown anddescribed, and accordingly, all suitable modifications and equivalentsmay be regarded as falling within the scope of the invention in theappended claims and their equivalents.

1. A communication system for communicating data, comprising: atransmitting device including a coder for encoding data of a primarysignal to generate encoded data such that polarity of the encoded dataalternates between positive and negative polarities, a polarity-reverseddata generator for reversing the polarity of part of the encoded data togenerate polarity-reversed data, and a transmitter for transmitting, ascommunication data, the encoded data including the polarity-reverseddata; and a receiving device including a receiver for receiving thecommunication data, a polarity-reversed data detector for determiningwhether or not polarity of the received communication data alternatesbetween positive and negative polarities, and detecting, as thepolarity-reversed data, data of which the polarity differs from anexpected polarity, and a polarity recognizer for recognizing thepolarity of the polarity-reversed data and treating the recognizedpolarity as control information.
 2. The communication system accordingto claim 1, wherein the coder generates the encoded data by convertingthe primary signal n bits by n bits into an m-bit data unit (n<m) whosepolarity alternates between positive and negative polarities.
 3. Thecommunication system according to claim 2, wherein the polarity-reverseddata generator generates the polarity-reversed data by reversing thepolarity of one of the m-bit data units constituting the encoded data,and the polarity recognizer determines whether the polarity of thepolarity-reversed data is reversed in a positive-to-negative directionor a negative-to-positive direction, and treats 1-bit informationindicated by the determined reversal direction as the controlinformation for the receiving device.
 4. The communication systemaccording to claim 2, wherein the polarity-reversed data generatorgenerates the polarity-reversed data by reversing the polarity of atleast one of the m-bit data units constituting the encoded data, and thepolarity recognizer recognizes, as a start trigger of the controlinformation, the polarity-reversed data that is detected first in thereceived communication data, and treats the polarities of k m-bit dataunits succeeding the first detected polarity-reversed data as thecontrol information.
 5. The communication system according to claim 2,wherein the polarity-reversed data generator generates thepolarity-reversed data by reversing the polarities of at least two ofthe m-bit data units constituting the encoded data, and the polarityrecognizer recognizes, as a start trigger of the control information,the polarity-reversed data that is detected first in the receivedcommunication data, treats the polarities of k m-bit data unitssucceeding the first detected polarity-reversed data as the controlinformation, recognizes (k+1)th polarity-reversed data aserror-correcting code data, and checks normalcy of transmission linebased on the error-correcting code data.
 6. The communication systemaccording to claim 2, wherein, when the transmitting device transmits aresponse message to the receiving device in response to data receivedfrom the receiving device, the polarity-reversed data generatorgenerates the polarity-reversed data by reversing the polarity of one ofthe m-bit data units so as to indicate a start position of the responsemessage, allows the polarity of the m-bit data unit immediatelysucceeding the start position of the response message to remainunreversed if the response message to be sent is a normal responsemessage, and reverses the polarity of the m-bit data unit immediatelysucceeding the start position of the response message if the responsemessage to be sent is an error response message, and the polarityrecognizer recognizes, as a start trigger of the response message, thepolarity-reversed data that is detected first in the receivedcommunication data, and determines based on the polarity of the m-bitdata unit immediately succeeding the first detected polarity-reverseddata whether the response message is a normal response indicative ofnormal transmission of the data or an error response indicative oftransmission error.
 7. A communication system for communicating data,comprising: a transmitting device including a coder for encoding data ofa primary signal to generate encoded data such that polarity of theencoded data alternates between positive and negative polarities, a headtiming assigner for assigning, to the encoded data, head timingindicative of beginning of the encoded data, a polarity processor forperforming a process on k data units succeeding the head timing suchthat polarities of the k data units are individually reversed or leftunreversed, and a transmitter for transmitting, as communication data,the encoded data to which the head timing has been assigned and of whichthe polarity has been processed by the polarity processor; and areceiving device including a receiver for receiving the communicationdata, a head timing detector for detecting the head timing from thecommunication data, and a polarity reversal/non-reversal detector fordetermining whether or not the polarities of the k data units succeedingthe head timing alternate between positive and negative polarities,detecting the polarity different from an expected polarity as a polarityreversal value and the polarity identical with an expected polarity as apolarity non-reversal value, and treating polarity data constituted byat least one of the polarity reversal and non-reversal values as controlinformation.
 8. The communication system according to claim 7, whereinthe encoded data is assembled into packets, the head timing assignerassigns the head timing to each of the packets, the polarity processorperforms a polarity process on a desired number of data units succeedingthe head timing of each of the packets so that different packets mayinclude respective control information corresponding thereto, and thepolarity reversal/non-reversal detector acquires, as the controlinformation on the respective packets, the polarity data that variesfrom packet to packet.